US 3035590 A
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United States Patent C) 3,035,590 AIR SUPPORTED STRUCTURE Edward Neil Helmets, Newark, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Oct. 31, 1958, Ser. No. 770,959 Claims. (Cl. 13S- 1) The present invention relates to portable shelters and, more particularly, to air supported shelters having the shape of a section of a sphere, c g., a hemisphere or a spheroidal section being more or less than a hemisphere.
Air supported shelters consist in brief, of a film, fabric, or similar material of low air permeability, anchored or otherwise fastened to the ground or other suitable surface and maintained in the erected state by air pressure. Provisions for ingress and egress and lighting of the interior are made, which provisions maintain the structure in a substantially pressure-tight condition. Structures up to about l0() feet in diameter have been constructed successfully. However, at diameters greater than about 100 feet, the ination pressure necessary and the upward force caused by the velocity of wind striking the structure combine to provide stresses zthat currently-known fil-ms, fabrics, etc. cannot withstand.
Itis the primary object of the present invention to provide a design for air supported structures having the shape yof a spheroidal section that will enable such structures 4to withstand extremely high forces. A 'further object is to provide a design that will permit construction of air supported structures having diameters of 300 feet and higher that can withstand wind velocities of 70 `miles per hour and higher.
Other objects and advantages of the invention will be readily apparent from the following detailed description when read in conjunction with the accompanying drawing, wherein:
FIGURE l is a view in perspective of the preferred embodiment of Ithe inated air supported structure of the present invention.
FIGURE 2 is a sectional view of the air tight means employed to secure the lower edge of the inflated air supported structure.
Briefly stated, the present invention contemplates an air supported structure having the shape of a spheroidal section comprising a` plurality of gores of llexib'ie material (lrn, fabric, and `the like) having a common apex, the distance from the apex to both extremities of the base of each of said gores -being less than the distance from the apex to a point halfway between the extremities of the base of each gore; the structure having its lower edge secured by substantially air-tight means. The limitation on the distances from apex to base provides a structure having a parachute-like appearance and one in which the lower edge has a scalloped appearance. Y
In one mode of carrying out the present invention, a substantially heniispherical sheet of film, tailored to provide the aforementioned gore sections of reduced radius, is pegged Ito the ground at its lower edge. Having been securely staked, the interior is inflated lb-y moderate air pressure using a centrifugal fan. The shelter, thus formed, has a segmental shape due to .the critical tailoring of the gores, Its lower edge appears scalloped when viewed from above. And the shelter, at its top, converges to form a single dome and apex. One lor more doors, each in the form of an air lock, may be arranged at suitable points around the base of the structure depending upon the ultimate use of the structure. For Ithe purpose of lighting, the lm or fabricemployed or Apanels or portions thereof may be transparent or translucent. Alternatively, articial lighting may be used.
The supply of air required to maintain inflation is small in comparison to that required to inflate initially. Since 3,035,590 Patented May 22, 1962 ICC it is desirable to have a moderate amount of air leakage `to provide ventilation within the structure, the amount of air required is that necessary to replace the amount lost due -to leakage. The pressure required to maintain the structure erect under normal conditions is very low, being of the order of about .O2-.03 1b./ sq. in. However, when high winds are anticipated, then pressures up to 0.1 lb./sq. in. may be used.
Referring to FIGURE 1 of the drawing, the structure formed in accordance with the present invention is composed of a plurality of sections or gores 11 arranged substantially in the form of a hemisphere 10. The lower edge of the hemisphere appears scalloped due to the critical limitation imposed upon the gore sections; namely, that the distance from the apex of the hemisphere to the extremities of the base of each gore be less than the distance from the apex to a point on the base of the gore halfway between the extremities of the gore.
The reduced radii sections or gores may be obtained in several ways. The fabric or lm may -be a single sheet tailored to provide the aforementioned gores as in# tegral sections when inated. Alternatively, the fabric or film may be in the form of a plurality of gores stitched or adhered together to provide the structure of the inven'- tion upon inilation. Alternatively, the fabric or film may :be a single sheet that is capable of elastic deformation. When such a smooth surface sheet is anchored to the ground by means of cables or load-carrying members extending from the center of the sheet to its outer extremities, the smooth surface upon inflation assumes a parachute-like shape -due lto restriction by the cables and simultaneous deformation due to stretching of the material between Ithe cables. When cablesy are used, the structure tends to assume 'the shape of an oblate spheroid rather than a section of a sphere,
The preferred embodiment of the present invention, as
v shown in FIGURE 1, utilizes `a combination of tailoring and elastic deformation due to the restricting load-carrying members (cables 12) to provide the cri-tical appearance of the invention. The cables 12 extend from a crown 13, which may -be of metal or other suitable material, to the foundation y14 ofthe structure.
The method of constructing the foundation is to dig a circular trench i9 of ythe necessary Width and depth corresponding to the circle obtained by connecting the points representing the extremities 20 of the gores; driving a circular pipe 21 into the trench 19; and then tucking the base of the film under the pipe to make the structure substantially air-tight at the base. Instead of a pipe as described, wooden piles, concrete piles, concrete footers, or ground :anchors may be used in a similar manner to achieve the same purpose. Upon inflation-the structure takes on its characteristic appearance with the scalloped edge at ground level as shown in the figure.
An entrance 15 is provided with two doors; the outer one is shown at i6. The inner door, not shown, serves to keep the structure air-tight when the outer door 16 is open. Aperture-s 17 are provided to equalize the pressure when it is desired to open the doors. A centrifugal pump 18 provides the air necessary to maintain ination of the structure and to supply ventilation within the structure.
i As materials for the structure, any lm or fabric, coated or uncoated, capable of supporting itself upon inflation, having slight permeability and being capable of weathering the elements may be used. Mylar 1 polyester film, uncoated or coated, is a preferred lilm for the structure.' Nylon fabric coated with a vinyl resin or impregnated with neoprene, Buna rubber or Hypalon2 are among 1 Manufactured by E. I. du Pont de Nemours & Co.
2A synthetic rubber manufactured by E. I. du Pont de Nemours.
1ies'ults are given in Table 2.
the useful fabrics that may be used. As load-carrying members (the cables), steel bands, steel cables, Mylar polyester lm strips or rope, nylon rope, hemp rope, etc. may be used.
The air supported structure of the present invention has Vbeen described as being a spheroidal section. One obvious deviation is the scalloped lower edge, as described, due to the construction of the gore sections. In designing the gore sections, two basic gore designs are possible: constant gore radius and decreasing gore radius from base to apex. Theoretically, a structure with constant gore radius has uniform strength from the bottom to the top of the gore, the tension on the lm or fabric under a given load being proportional to the gore radius. Theoretically, the structure in which the gore radius decreases from the base to the apex is capable of withstanding greater pressure near the apex than at the base of the structure. Since tests indicate that the maximum aerodynamic lift occurs near the apex, this latter design (wherein the gore radius decreases from the base to the apex) is preferred.
The most desirable structure, as mentioned previously, is one in which cables from apex to base are used. Upon iullation, it has been found that the cables do not assume the shape of a circular arc, but rather assume a shape that is flatter at the apex and steeper at the base, i.e., an oblate spheroid.
In the following examples, air supported structures of this invention are compared to conventional air supported structures. T e results indicate that a drastic improvement in the strength of air supported structures can be obtained by the structures of the present invention.
EXAMPLE I members were 9&6" stranded steel cables fastened at the crown to a 3-inch diameter li-inch steel plate. The structure was inated to a pressure of 1.27 p.s.i. and no failure occurred.
As a control, a hemisphere of 0.5 mil Mylar polyester film having a diameter of 42 inches at the base and Vbeing 14 inches high when in-llated, was inflated until the structure failed. Results are given in Table 1.
T cible I Maximum Calculated Example Initiation Pres- Stress at sure, psi. Failure Control o. 7a 16,500 psi.
1. 27 Did not fail.
EXAMPLE n A scalloped air supported structure of this invention having 24 gore sectionsrof 0.25 mil Mylar polyester film, 42 inches in diameter at the base and 14 inches high when inflated, was tested in a wind tunnel, The 23 load carrying members were/ stranded steel fastened at the crown to a 3-inch diameter 1A steel plate.
. As a control, a hemisphere of-G.25 mil Mylar polyester film, 42 inches -in diameterV at the'base and 14 inches highY wheninilated, was also tested in the wind tunnel.
l Pi/Q=ination pressure over impact wind pressure.
Calculations indicate that the advantages apparent for the experimental models tested in the examples will provide the basis for construction of similar structures within the scope of the present invention having diameters of at least 1G() feet and up to 300 feet or higher and capable of withstanding air velocities of at least 70 miles per hour. Such structures will find wide use as construct-ion shelters, swimming pool enclosures, etc.
It is anticipated that if the structure is to be used over an extended period, then it may be advisable to erect a framework within lbut not necessarily in contact with the normally air-supported structure. In this event, any emergency, e.g., power failure, would not cause complete collapse of the structure. Such a framework might be a simple wooden or metal construction erected to conform substantially to the inside contour of the structure or as slats placed within sleeves in the structure as ribs Inr'lated and sealed tubular sleeves might also be used to function as ribs to prevent complete collapse.
It should be understood that although the examples describe structures wherein 16 and 24 gore sections were used, any number greater than about 4 will provide the advantages of the prment invention. T-he important consideration is that by reducing the radius over which the inating pressure is applied (by using gore sections), the tension in the film or fabric, being proportional to the gore radius, is similarly reduced.
It should also be understood that the invention is applicable not only to lair supported structures entirely in the form of spheroidal sections, but to supported structures composed partially of spheroidal sections. Thus, the invention is yapplicable to a structure in the form of a lcylindrical section having spheroidal sections at each end. The spheroidal sections can be modified in accordance with the present invention.
As many widely diierent embodiments of `air supported structures may be constructed within the spirit yand scope of the invention, it is understood that the invention is not to be limited except as defined in the appended claims.
What is claimed is:
l. A structure supported solely by air pressure in the interior thereof, said structure comprising a plurality of gores of exible material terminating in a lower edge; said gores having a common apex, having `a gore radius `which decreases from the base to the apex and arranged to give said structure the form of a section of aY sphere; the distance from the'apex of said gores to the extremities of the base of each of said gores being less than the distance from said apex to a point on the base halfway between the extremities of the base of each of said gores; and means for rendering the lower edge of said structure air-tight.
2. A structure-as in claim l wherein cables extend from the apex of saidstructure to the base of said structure along lines which define said gores. Y
3. A structure as Iin claim l composed of Mylar polyester film.
,4. A structure as in claim l having a diameter of at east 1GO feet. a
5. A structure supported solely by air pressure in the interior thereof, said structurercomprising a plurality of gores of flexible, self-supporting, weather resistant, slightly permeable material terminating in a scalloped lowerY edge; said gores having a commonV apex, having a gore radius rwhich decreases from the base to the Iapex and arranged to give said structure a substantially hemispherieal form; the distance from the apex of said gores to the extremities of the base of each of said gores being less than the distance from said apex to a point on the base halfway between the extremities of the base of each of said gores; Iand means for rendering the lower edge of said structure air-tight.
428,697 Rumrille May 27, 1890 Lanchester Apr. 29, 1919 Silverstein Oct. 5, 1926 Nei Nov. 30, 1943 Cloud Dec. 13, 1949 Suits Aug. 18, 1953 Hasselquist Sept. 8, 1953 Smith Jan. 17, 1956 Mackey Feb. 10, 1959 FOREIGN PATENTS France June 25, 1929